Last weekend Dominique and I made this short tutorial on how to exposure your camera when using a log gamma picture profile, such as Sony S-log or Canon C-log. After we finished filming I took the Lastolite "18%" gray target home and measured its reflectance versus the gray cards I bought. It turns out that the Lastolite product is actually about 15% gray (a bit darker) and the R-27 gray cards I bought are almost exactly 17.7% (what "18% gray" is really supposed to be). So the cards are the more accurate way to go. The Lastolite target will cause an over exposure of 0.2 stop, which is sort of in the noise when it comes to exposure with log gamma picture profiles.
From a practical point of view you're perfectly OK using either. In fact, S-log usually likes to be a bit over exposed from a camera noise standpoint. You're going to color correct the picture either way. Since S-log3 is so linear all you need to do it make a slight gain adjustment and you're there - easy.
After doing this tutorial I found out a lot more about the history of 18% gray cards. I'll share that in the next post.
HOW WE DID IT: Doc Style
2 years ago